Tom O’Connor, the longest-serving Division I athletic director in the area who oversaw George Mason basketball’s rise to national prominence and the university’s move to the Atlantic 10 last year, will step down this summer.

O’Connor, 67, will relinquish his duties June 30 and remain in a fundraising role until January. His contract was to expire in June 2015. George Mason, which sponsors 22 sports, will begin the search for a replacement right away.

“I have been thinking about it, and in January, I asked to meet with our president, Angel Cabrera,” O’Connor said. “I told him I was considering a change in lifestyle. . . . I’ve been watching other people’s grandchildren compete in college for a long time. I want the opportunity to see my [10] grandchildren compete now.”

O’Connor arrived at the Fairfax campus in 1994 after running the athletic departments at Loyola (Md.), Santa Clara and Saint Bonaventure. Previously, he coached men’s basketball at Dartmouth (1970-74) and Loyola (1974-76).

During O’Connor’s tenure in Fairfax, George Mason’s stature in men’s basketball, the university’s foremost program in the absence of a football team, reached new heights when the Patriots advanced to the 2006 Final Four. Under Coach Jim Larranaga, they became a heavyweight in the Colonial Athletic Association and advanced to the NCAA tournament five times.

O’Connor served on the NCAA Division I men’s basketball committee from 2004 to ’09 and was chair in 2007-08.